I had a pair a few years back and the sonics were superb. I still have yet to hear the type of huge soundstage these amps threw, along with great bass and superb detail driving my Wilson Sophia speakers. I also used a pair of Zero autoformers to raise the impedance of the speakers, something you should strongly consider, especially if your speakers are a difficult load (i.e. low impedance, impedance dips, reactive load, etc.). The main drawbacks are their ability to double as a space heater--each monoblock draws 5 amps at idle, so you may want to consider a separate AC circuit for each. I also had problems with mine from time to time where one channel or other would get weak and fuzzy. I seemed to remedy this by cleaning each tube socket and re-tensioning the tube pin socket springs, which was a relatively easy but time-consuming job. If you are not into having to do what might turn out to be some maintenance on them, you may not want to go this route. If it were my choice I would stick to a current model like the Atma-Spheres, which have a reputation for far greater reliability. I also know a few other Panthere users who you might speak with, so if you e-mail me I will give you their e-mail addresses.
